This invention relates to digital audio/visual reproducers or EDL players. More particularly, the present invention relates to a method for maintaining edit decision lists of digital audio/video reproducers to maintain synchronization across timecode edits.
Picture and sound editorial work for movies and television is currently done, for the most part, on digital workstations. These workstations may use a xe2x80x9cflat filexe2x80x9d format in which all of the elements are grouped into a single and relatively long file. When sound editorial work is done on physical media, such as film, the sounds are cut with blank film, called leader, between film. The result is equivalent to a flat file. Modifying the sound track requires splicing the film. This is often called destructive editing.
Another workstation format is known as xe2x80x9cedit decision listxe2x80x9d (EDL) using an EDL digital audio reproducer (EDL player). In the EDL format, a small file of text information references a number of elements in individual audio files by the elapsed time. The entries in the EDL describe the attributes of each edit and the file name of the new clip. The digital audio/video reproducers that use EDL""s reproduce audio/video locked to a continuous stream of timecode imprinted on the film by playing segments of audio/video in a seamless sequence. The length and location of these segments is determined by entries in the EDL. The method of joining the segments may be either a programmed cross-fade or a hard splice. Typically, in audio editing, the entries are cross-faded to avoid audible pops and clicks caused by sudden steps at edits.
Once the editorial work is done, the results may then be stored in a flat file. This may be done directly for video or sound. In the case of film editorial done on AVID or similar systems, a negative cutting list is generated. The film negative is cut to match the EDL. In a typical EDL player, sounds are buffered for some time in advance, perhaps several seconds. When a segue from one sound clip to another is done, a cross-fade is computed and the incoming cross-faded sound clip is appended to a buffer in the EDL player.
EDL""s are known as a non-destructive editing format. By manipulating a list, two distinct advantages are gained over the flat file format. First, changing reference files allows quick and easy editing. Second, by not copying files to perform edits, time and storage space are saved.
Position information and rate information are required to play back digital audio in synchronization with the video. Once the position in the EDL is established, the EDL player opens the appropriate sound clip on the appropriate sample. The rate information determines the rate at which samples are drawn from the file, Thus, EDL""s allow large amounts of data to be manipulated by modifying only a small list, saving time and storage space during editorial work
However, implicit in the design of an EDL player is that the position information, i.e. timecode, will be sequential. Behavior at timecode discontinuities is unpredictable. Discontinuities in position are dealt with in an unspecified manner, for example, a likely result of timecode position discontinuity could be a momentary mute of indeterminate length while the current clip or file was closed and the appropriate clip was opened.
Thus, although EDL player""s present several advantages, position information such as timecode must be continuous for their proper operation. Digital audio/video reproducers that use EDL""s are therefore not appropriate for use in applications where timecode is discontinuous. Subsequent splicing or other damage to the film can disrupt the continuity of the positional timecode and cause the momentary mutes described. One such instance is theatrical exhibition of timecoded films having trailers and splices.
Systems have been devised to address this and similar problems. For example, one method of playing back audio to discontinuous timecode essentially uses the timecode itself as the EDL. When a discontinuity is detected, audio from the new file is appended to the buffer according to the new timecode. Although this method is simple, the edits are not cross-faded. In the case of APT compressed digital audio data, such as the DTS digital theater system, an unintentional cross-fade occurs because of the nature of the compressor. If this method were used with uncompressed digital audio data it would click and pop at edits. Another system requires a pass of the timecode to record an edit. A second pass is required for the next edit. Thus, real time continuous edits are not achieved.
Accordingly, there is a need for a method of maintaining edit decision lists for EDL players to maintain synchronization across timecode edits. The present invention fulfills this need and provides other related advantages.
The present invention resides in a system and method of generating continuous position reference, i.e. timecode, locked to an incoming discontinuous position reference for input into an EDL player (audio/video reproducer). The edit decision list of the EDL player is maintained in real time so that the audio or video output corresponds to the discontinuous incoming timecode.
The system for maintaining the edit decision list for the EDL player includes receipt of a potentially discontinuous position reference, an edit decision list driven audio/video player, means for measuring position reference discontinuities, such as an edit identifier, means for generating a continuous position reference to drive the edit decision list driven audio/video player, such as a timecode generator, and means for using the measurements to maintain the edit decision list, such as an edit decision list modifying program. The system of the invention ensures that the audio/video output from the player maintains proper synchronization and proper transitions between discontinuities. The discontinuities are detected, measured and the edit decision list maintained with one pass in real time. The system may be implemented into separate nodes of an asynchronous network.
The system generally operates by first receiving a timecode. A discontinuity is detected within the timecode and the edit decision list is searched for a corresponding timecode discontinuity. If a corresponding timecode discontinuity is not found in the edit decision list, the edit decision list is maintained by creating and adding a timecode corresponding to the detected timecode discontinuity. The initial position in the edit decision list is located using the received timecode. The discontinuity is searched for by comparing the edit decision list to the time discontinuity. Dropouts and errors in the timecode are detected and corrected and a sequential timecode is generated which incorporates the corrected dropouts, errors and created corresponding time discontinuity timecode. A selected segment of digital audio/video is opened using the sequential timecode and a continuous audio/video stream is created from the maintained edit decision list.
Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.